The proper maintenance of an automobile or truck requires that the fluid levels be maintained at or above a prescribed level. Conventionally, an ullage rod or dipstick is used to measure the fluid level preferably at periodic intervals or realistically whenever the operator remembers to perform this function. It has been previously proposed to automate the measurement functions by electrically sensing the levels each time the vehicle is used. In particular, as shown in the U.S. Pat. Nos. 3,918,306, 4,373,389 and 4,594,893, it is known to use elongated capacitors in the oil reservoir and extending over the expected range of oil level. The capacitance will vary according to the oil level to provide a measure of oil level but is also dependent on the dielectric constant of the oil. It is important to compensate for variations in the dielectric constant since it can vary considerably with different brands of oil and the usage of the oil. Compensation has been provided heretofore by employing a second capacitor which is always submersed in the oil and coupled in circuit with the level sensing capacitor in a way to compensate for any change of dielectric constant.
It is desired to use the compensated capacitance scheme to obtain the advantages thereof but to avoid the cost penalty of a second capacitor.